Most important requirements of next-generation wireless access systems are to support high data throughput. For this, a variety of technologies such as MIMO (multiple input multiple output), CoMP (cooperative multiple point transmission), relay, etc. have been developed.
Conventional wireless access systems consider only a single carrier although different bandwidths are configured for uplink and downlink. For example, there has been provided a single carrier based wireless communication system in which uplink and downlink are respectively composed of a single carrier and an uplink bandwidth and a downlink bandwidth are symmetrical.
To secure a wide bandwidth for satisfying higher data throughput in consideration of saturated frequency resources, carrier aggregation (CA) (multiple cells), which aggregates a plurality of dispersed bandwidths and is designed to satisfy basic requirements that independent systems are respectively operated using the bandwidths, has been introduced.
Here, a carrier for a bandwidth, which can be independently operated, is referred to as a component carrier (CC). To support increasing transmission capacity, 3GPP LTE-A or 802.16m extends the bandwidth thereof to 20 MHz or more. In this case, one or more component carriers are aggregated to support a wide bandwidth. For example, if one component carrier supports a bandwidth of 5 MHz, 10 MHz or 20 MHz, a maximum of five component carriers are aggregated to support a system bandwidth of up to 100 MHz.